Cathode-ray tube beam-positioning device



April 7, 1953 N. KAFKA 2,634,381

CATHODE-RAY TUBE BEAM-POSITIONING DEVICE Filed March 26, 1951 ROTATABLE 3 PERMANENT NON-MAGNETIC IO MAGNET F 2 M NTI PL I: 2 '5 CU NG ATE K '6 l4 DEFLECTION YOKE ROTATA BLE l3 PERMANENT MAGNET YINVENTOR. NICHOLAS KAFKA ATTORNEY Patented Apr. 7, 1953 CATHODE -RAY TUBE BEAM-POSITIONING DEVICE Nicholas Kafka, Bellwood, Ill., assignor to Zenith Radio Corporation, a'corporation of Illinois Application March 26, 1951, Serial No. 217,605

4 Claims.

This invention relates generally to electronbeam positioning or centering devices, and more particularly to a positioning device for a cathode ray tube which enables the electron beam developed within such a tube, when in its undeflected position, to impinge on any desired point of the target or screen electrode of the tube.

A cathode-ray tube for use as a reproducing device in a television receiver, or for other related purposes, includes a source of electrons located in the neck portion of the tube and a screen or target electrode situated in the conical portion thereof opposite the electron source. Suitable electrodes are included in the tube for focusing the electrons emitted from the source into an electron beam and for directing the beam to the screen electrode. An electro-static or electro-magnetic arrangement is also included within the tube or supported on its neck portion for deflecting the electron beam to scan it over an area of the screen electrode. Moreover, an electro-static or magnetic assembly is usually provided for focusing the electron beam to enable images to be reproduced on the screen with clarity and distinctness.

It has been found desirable to provide some means for positioning the electrons beam in order that images may be reproduced correctly centered on the screen area despite slight misalignments of the component elements of the tube. One known beam-positioning arrangement comprises means for adjusting the angular position of the'focusing device of a magnetically focused tube relative to the longitudinal axis of the tube. However, such structure is usually awkward and commercially infeasible and, obviously, is not applicable when electro-static focusing is utilized.

Another beam-positioning system for an electro-magnetically deflected type of tube consists of suitable circuits for passing a controllable unidirectional current through the lineand fielddeflection windings of the yoke. The amount of current passing through the respective windings is adjusted by a control until the electron beam is accurately centered on the screen. This arrangement has been found to be satisfactory in netic type which is simple to construct and is convenientlyadjustable to perform its centering function.

Yet another object of the invention is to provide an improved and inexpensive beam-positioning device which is especially useful for electrostatically focused cathode-ray tubes.

The beam-positioning device of this invention, for use in conjunction with a cathode-ray tube having a target or screen electrode mounted at one etxremity and means at its other extremity for generating and directing an electron beam along a given path to the target, comprises a supporting structure mounted in a plane transverse to the electron path, and at least one bar magnet exhibiting north and south magnetic poles at its respective extremities and mounted on the supporting structure for rotation about an axis laterally displaced from the path. A pole piece is mounted on the supporting structure between the magnet and the electron path to establish a beam-centering field within the tube traversing the path of the electron beam and having an intensity and sense determined by the angular orientation of the magnet.

The features of this invention which are believed to be new are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description when taken 'in conjunction with the accompanying drawing,

in which:

Figure 1 shows one embodiment of the invention associated with a cathode-ray tube, and,

Figure 2 shows a view taken along the lines 22 of Figure 1.

As shown in the drawing, a cathode-ray tube [0 has a target or screen electrode ll affixed to the end of its enlarged or conical portion, this target usually taking the form of an electronresponsive fluorescent screen. The tube also includes means [2, such as a conventional electron gun, located at the end of its neck section remote from target II for generating an electron beam and for directing the beam along a given path to the target, and an electro-static lens arrangement 12a, [219, I20 (for example) for focusing the beam on the screen. A deflection yoke [3 of any well-known construction is mounted on the neck of tube I0 adjacent the conical section to deflect the electron beam and scan it in a preselected two-dimensional pattern over an area of target H,

\ a Thebeam-positi'oning device of this invention foraccurately locating the scanning pattern within the confines of screen ll comprises a supporting structure or plate of non-magnetic ma- 'terial whichis mounted on the neckse'ction of tube I adjacent deflection yoke I 3 as shown. Structure I 4 may be rigidly held on the neck section by providing a friction fit therebetween or by means of any well-known mounting brackets. Plate l4 has a permanent bar magnet 15 exhibiting north and south poles at its respective extremities rotatably secured thereto by means of a pin I 6 about an axis laterally displaced from the electron path within the tube. The magnet is held in frictional engagement with the plate by the pin so that upon rotation thereof to a desired angular position it is firmly held in such position. A pole piece I1 is secured to mounting plate 14 between magnet l and the neck section of tube [0 to direct the field from'themagnetacross the axis of the tube. In this manner a first. beamecentering field is developed "within the tube, traversing the path of the electron beam. Rota? tion of magnet 15 does not affect the direction of the; above-mentioned beam centering field since its direction .is fixed by pole piece t1- However, the intensity and sense of the field are determined by the. angular orientation of the'mag-net. For when the north pole of the magnet is aajacent the, pole piece, rotation of the magnet through 180 -can.increasef.the field from zero to maximum intensity in onesense and back to zero. Whereas, when the south-pole. is adjacent the pole piece rotation of the magnet varies thev field intensity but .in'the opposite sense.

Plate I '4fhas a'f-urther magnet l8 secured therewbymeans of a pin l'9 for rotation about an axis laterally displacedffrom the electron path in tube Ill and angularly displaced from the .axisoj magnet 15 bysubstantially'90.. Magnet 1.8 may also be a bar magntmagnetized in a longitudinal direction s'o that one end "i'sfa north pole and the other a, south 'pole, as shown. Magnet [8, like magnet l5, is ffrictiona'lly. held against plate I4 by its associated'pinso that it may be set, in any desired position. .A polepiece 20 is secured to the mounting plateIbetween magnet l8 and the neck section of tube 10 to direct the magnetic field from this magnetac'ross .th'eaxis of the tube. The latter arrangement developesa second beam-centeringfieldwithin'the'tube, traversingthejpathlof the .electronbeam, at substantially rightan'gles .to the first-describedbeam-centeringfield. The intensity and sense of -the second beam-centering fieldjmay be adjusted by rotation of magnet l8 aboiitits axis,

The beam-positioning, device developes, therefore, two magneticfields extending across the pathv of theelectronbeam and mutu'a'llydi'sposed at right angles. The intensity andvsense of each of these fields can be adjusted simplyby rotating magnets l5;and il811ntil a desired resultant field is obtainedof proper sense and magnitude toposition accurately .the electron beam on target! I The inventionprovides, therefore, anextremely simple devicetor positioning an electron beam within acathode-raytube. The device may be constructed in an economicalmanner-andis.composed of relatively few and inexpensive compo.- nents; Moreover, the .deviceprovides an extremely convenient means. for. positioning-an electron beam, this being accomplished, by the mere manipulation of "the. 'two.:ba-r magnets which vare mounted to be readily accessible when the. tubesi's mounted in place in a television receiver, :orglike apparatus. The device. has been constructed and has been .found to operatewith a high "de reegof satisiactioninpertorming its centeringjunction.

While a particular embodiment of the invenmay be made and it is intended in the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

I claim:

1. A beam-positioning device for a cathode-ray tube, having a target electrode and means for generating. and directing an electron beam along a given path to said target, comprising; a supporting structure mounted in a plane transverse to said path; at least one bar magnet mounted on said structure for rotation about an axis laterally displaced from said path and exhibiting north and south magnetic poles at its respective extremities; and a pole piece mounted on said supporting structure between said bar magnet-and said path in an asymmetrical position relative to said path for establishing a beam-centering field within said tube traversing said path with an intensity and sense determined by the angular orientation of said magnet. I

2. A beam-positioning device for a. cathode-ray tube, having a target electrode and means for generating and directing an electron beam along a given path to said target, comprising: .a first bar magnet mounted for rotation about an .axis laterally displaced from said path .and exhibiting north and south magnetic polles. at its respective extremities; a first pole piecedisposed between saidfirst bar magnet and said path in an asymmetrical. position relative to. said path for ,estab.- lishing .a. first beam-centering. field within said tube traversing. said path with any intensity and sense determined by the angular orientation of said firstmagnet av second bar magnet mounted for rotation about an-axisla'terally displaced from said pathand angularly displaced from saidfirstmentioned axis, said secondbar magnet exhibiting north and south magneticpoles atits respec: tive extremities and a second polepiece disposed between said second bar magnet and said path inwan asymmetrical position relative to .said path for establishing a second beam-centering field within said tube traversingsaid path at a selected angle to said first beam-centering field and having an intensity and sense determined by the anguilar orientation of said second magnet.

3. A beam-positioningdevice .for a cathode ray tube, having a. target. electrodev and means for generating. and directin an electron beam along. av given path to. said. target, comprising: asupporting structure mounted-in a plane trans versetov said path; a first. bar mag-net mounted onlsaidstructure .ior rotation aboutan axis .laterally displaced from. said path and exhibiting north and .south magnetic polesuat itshrespective extremities a first pole piece .mounted on -.sai d supporting -structure betweensaid (first bar mag- .net and said-path in anrasymmetrioal position .relative to-said path ;;for establishing a firstibeamrcenterin field within saidstube -traversing..-said path with. an intensity and..-sense-.determined the angular -orientation ofssaidfirstf magnet; :a second Ibar magnet Imoun'ted' on .s'aid structure for irotation about an axis 'laterallydisplaced from said -path and angularly displaced f-rom said first-mentioned axis, said second bar-magnet exhibiting north and south magnetic poles at its "respective extrer-nilties; 'and'a second pole piece mounted on said "supporting structure between said second bar magnehfihd said .path in an symmetrical position relative. to said pat1 i. for es'tablishingla second beam-centering held withinsaid, tube traversing. saidtpa-th. at a -.selected tionlhasbeengshown anddescribed; modifications (5 angle to Said fir b amen ring fi ld fln l fivf ing an intensity and sense determined by the angular orientation of said second magnet.

4. A beam-positioning device for a cathode-ray tube, having a target electrode and means for generating and directing an electron beam along a given path to said target, comprising: a sup porting structure mounted in a plane tranverse to said path; a first bar magnet mounted on said structure for rotation about an axis laterally displaced from said path and exhibiting north and south magnetic poles at its respective extremities; a first pole piece mounted on said supporting structure between said first bar magnet and said path for establishing a first beam-centering field within said tube traversing said path with an intensity and sense determined by the angular orientation of said first magnet; a second bar magnet mounted on said structure for rotation about an axis laterally displaced from said path and angularly displaced from said first-mentioned axis by an amount substantially equal to 90, said second bar magnet exhibiting north and south magnetic poles at its respective extremities; and a second pole piece mounted on said supporting structure between said second bar magnet and said path for establishing a second beam-centering field within said tube traversing said path at right angles to said first beam-centering field and having an intensity and sense determined by the angular orientation of said second magnet.

NICHOLAS KAFKA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

